Method and apparatus for perforating well casings



July 21, 1959 R. F. KRUEGER EI'AL 2,895,554

METHOD AND APPARATUS FOR PERFORATING WELL CASINGS Filed Nov. 5, 1954 a I 1 V, 4 .7 4 J v i Q .h i6 1 y C 1 1 Jal Hw 4 i UM 5n n United States Patent IVIETHOD AND APPARATUS FOR PERFORATING WELL CASINGS Roland F. Krueger, Fullerton, and Lee C. Vogel, Long Beach, Calif., assignors to Union Oil Company of California, Los Angeles, Calif., a corporation of California Application November 5, 1954, Serial No. 467,033 4 Claims. (Cl. 166-35) This invention relates to an improved method and apparatus for perforating well casings, and in particular concerns a perforation method which does not adversely affect adjacent subterranean formations.

In one type of well completion practice, a well casing is inserted into the bore so as to extend through the producing formation, and is held in place by forcing cement into the annulus between the casing and the walls of the bore. The casing and cement liner is then perforated at the level of the producing formation to provide channels for the fluid from the producing formation to enter the bore. Such channels are conventionally formed by means of a gun perforator, which is a device positionedopposite the production zone it is fired by electrical or percussive means.

As a result of a study of gun perforating techniques and detailed examinations of core samples which have been gun perforated in the conventional manner, we

have found that the channels formed through the casing and cement liner into the producing formation are by no means clear and unobstructed. In many instances such channels were found to be plugged with tightly packed drilling fluid solids so as to be relatively impermeable to oil flow. This is particularly true where the drilling fluid contains a high proportion of solids, e.g., in deep wells. An investigation of the cause of this phenomenon revealed it to be due in large measure to an eflect substantially identical to that of the familiar 'water hammer. When the perforator is fired while submerged in the drilling fluid, the high pressure and large volume of gas developed by the explosion forces the column of drilling mud above the perforator upwardly through the casing. Upon dissipation of the pressure such column of mud falls back through the casing until it meets the column of mud below the perforator whereupon it is stopped so abruptly that a shock wave is set up in much the same way that a shock wave or water hammer is created when a long straight column of water flowing under pressure is suddenly shut off at the point of discharge. The shock wave so produced is of such magnitude and is so oriented that it drives the drilling mud with great force into the channels formed by the perforating projectiles, and the drilling mud solids become tightly packed in said channels and form a permanent plug therein. As a consequence, the perforating operation is of limited success since, while it does effect the formation of channels or holes through the casing and liner, it immediately proceeds to plug up a substantial number of such channels or holes and thereby to a considerable extent defeats its own purpose.

We have now found that the above diflioulties can be obviated to a great extent by providing means which allow relatively free upward movement of the column of mud in the bore when the perforator is fired, but which ice restrict subsequent downward movement of the mud. More particularly, we have found that highly improved gun perforation results may be obtained by inserting in the bore above the perforator a special packer which is so constructed that fluid flow upwardlythrough the bore is substantially free but fluid flow inthe opposite direction is substantially restricted. With such'means in operation the fall of the mud column after detonation of the perforator is slowed down to such an extent that the aforesaid shock wave or hammer efiect is prevented. r

In the accompanying drawing which forms a part ofthis application, Figure 1 diagrammatically illustrates the principle of the invention and the means employed for applying the same; Figure 2 represents an exploded elevation, partly in section, of a packing device suitable for use in practicing the method of the invention; Figure 3 represents a plan view taken along line 33 of Figure 2; Figure 4 represents a plan view of the closure means of Figure 2; Figure 5 illustrates the operation of the packing device of Figure 2 during firing of a gun perforator associated therewith; Figure 6 illustrates the operation of said device subsequent to firingthe perforator; and Figures 7 and 8 represent plan and isometric views, respectively, of alternative closure means.

Referring now to. Figure 1, there is shown a bore hole 11 penetrating the earths surface into oil-producing formation 12. Well casing 13 extends substantially to the bottom of the bore hole and is secured to the Walls thereof by cement plug 15. A gun perforator 16 is suspended within the bore opposite formation 12 by means of a cable 17a depending from packer 18 inserted in the casing. Packer 18 is provided with a relatively large longitudinal passage 19 extending between its opposite faces and fitted at its upper end with a hinged closure 20. The latter is so arranged as to allow fluids to flow upwardly through passage 19 but prevents the flow of fluids downwardly therethrough. Packer 18 is provided with a second longitudinal passage 21 extending between its opposite faces, said passage 21 being of relatively small size so that the flow of fluids therethrough is substantially restricted. Cable 17 extending to the earths surface constitutes means for lowering and withdrawing packer 18 and perforator 16 into and out of the bore, and together with cable 17a may contain electrical conduits for firing perforator 16. Casing 13 is substantially filled with drilling fluid, not shown. As will readily be apparent, when perforator 16 is fired the sudden increase in pressure in the space below the packer will force the drilling mud upwardly through passage 19 in the packer, such movement being permitted by the hinged arrangement of closure 20. When the pressure has become dissipated to the point that it is equal to the hydrostatic pressure of the column of drilling mud above the packer, the mud will fall back down the casing. The weight of the mud, however, will close closure 20, thereby preventing the mud from passing downwardly through passage 19. Instead, the mud will pass through passage 21, and since the latter is of relatively small size the mud will descend back into the bottom of the hole relatively slowly and the aforementioned hammer elfect is avoided.

Referring now to Figures 2, 3 and 4 wherein like parts are designated by like numerals, the packing device therein shown comprises a solid body member 22 formed of a resilient material such as molded rubber. The upper portion of body member 22 takes the form of a cylinder having a diameter corresponding to the diameter 'of the well' casing in which the device is to be employed. The bottom portion takes the general form of'an inverted .cone which is coaxial with the cylindrical portion. A

truncated conical depression is hollowed out in the up- .mounted over rod '26. ping. rod 26 through the. central. passageway in body of cable 38.

per'face ofthe .body member to receiveclosure 23.

Body member 22 .is provided with four longitudinal.

I grooves 2.4 spaced 90 apart in the cylindrical walls of ,the body member to provide relatively small; passageways for the flow of fluids through the packer when the latter is inserted in a welli casing. Relatively large passageways 25, spaced 90 apart, extendlongitudinally i (through the bodymember, and likewise allow fluids to -fiow through the packer.

Also extending longitudinally through the body member is a central passagewayree alternative forms of packers of varying complexity may. likewise be employed. Thus, instead of the simple hinged closure structure herein described, suitably spring-loaded check valves may be employed. Simi1arly,-the packer may be constructed so as to'function as a. permanent pressure seal within the bore, e.g., it may be provided with .a' central passageway for the withdrawal of well fluids and with means for. latching theclosures or valves in closed position so that a differential, pressure may be ceiving threadedrod 26. The la'tteris provided at each end with means, not shown, for securing cables 27and 28; Closure 23 is formed ofiaflexible material, e.g.,

heavy sheet rubber, and takes the general form ofa having four lobes 29 attached to its periphery 90 apart. Said lobes are bent upwardly atan angle corresponding to the angle of the conical depression in the upper face of body member 22. Closure 23 is provided with a center hole '30 by meansof which it is The deviceis' assembled by slipmember 22 and then inserting the rod through. the central hole in closure 23' as shown. Washers 31 and 32 fits. tightly against the bottom and sloping sides of the depression in the :upper face of body member .22.

Figures 5 and 6 illustrate the operation of the packing' device of Figure '2' during and after firing the gun :perforator associated therewith, The packer is positionedin well casing 35 bymeans of cable: 36, and gun perforator 37 'is suspended below the packer by means by'forces the drilling mud upthrough the large passages 40 at'the upper-end 'of 'passages' 39 permitting the upward flow of fluid. therethrough, as shown in Figure ,5.

: are slipped over: the opposite ends of rod 26 and threaded I nuts 33 and 34 aretighteneddowm-so-thatclosure 23 25:

Immediately after the detonation the'pressure' dissipates and the column oi mud which has been-forced up through the packer will tend to fall back down the bore. I 'Asto such downward flow, however, the only path through the packet is via the relatively small grooves 41. Consequently, the downward flow of mud is relatively slow and there is no tendency to set up shock waves which would jam the mud solids. into perforations 42 in the casing and cause plugging of the same.

Figures 7 and 8 represent an alternative form of closure means in which the return path for the. mud' is via relatively smallholes 43 extending through the lobes of the closure. When such type of closure is employed .there is, of course, no need to provide grooves in the cylindrical surface of the packer as shown in Figure 2.

As will readily be appreciated, the packing device illustrated by the drawings is of extremely simple construction and etfectivelyaccomplishes the desired purpose of providing a substantially one-way path for the passage of drilling mud upwardly through the bore. In addition, this particular device may also be employed to swab out the casing after the perforating operation has been completed. We have found that when the cross-sectional area of the passages through which upward flow is permitted. constitutes a substantial proportion of the cross-sectional area of the casing it is not necessarythat the packer close off the casing with any great degree of precision. In some cases the packer may be constructed in such manner that the downward return path for the mud is merely via leakage around the edge of the packer, thereby obviating the need .for providing any positive element in the packer for such flow.

It will be apparent to those skilled in the art that while the packing device herein described is particularly adapted for the practice of the method of the invention, many maintained across the packer.

Othermodes of applying the principle of our inven-. .tion may be employed instead of those explained, change being madeas regards the method or apparatus employed provided the steps or elements-stated by anyof the following claims, or the equivalent of such stated steps:

or elements, be employed.

We, therefore, particularly point :out and distinctly claim as our inventioni 1 I 1. In a well completion process wherein well. perforating means are positioned .withina well borer, and are therein actuated toiperforatethe walls of the bore-said I means beingactivatedby. detonation of explosive and being submerged in abody: of solids-containing fluid .at

fluids downwardly. above said flow control means through the well bore.

' 2. In awell completion: device whereinwell perforat' ingmeans are positioned within a wellyboreandare actuated'therein to perforate the walls of :the b0l8, 1$2lld p means being activated by detonation of explosive and. being submerged in a body of solids-containing fluid at the timed detonation, a device for preventingthe solids in said fluid from plugging the perforations whichcom prises a flow; control device positioned 1 across the well I bore above said perforating means, saidflow control device including one way valvemeans to. permit how of said solids-containing fluid upwardly past said flow control device upon detonation of said perforating means,

and means to restrict flow of said fluid downwardly past said flow control device after detonation.

3. The device as set forth in claim 2, in which said well perforating means is a gun perforator comprising a plurality of projectiles capable of being propelled radi- References Cited in the file of this patent.

UNITED STATES PATENTS 1,248,689 McAvoy Dec. 4, 1917 1,362,838 Brandt Dec. 21, 1920 1,626,614 Kibele May 3, 1927 2,029,491 Lane Feb. 4, 1936 2,282,937 Bennett May 12, 1942 2,460,481 Abel Feb. 1, 1949 2,504,611 Zandmer Apr. 18, 1 950 2,530,966 Huber Nov. 21, 1950 2,562,458 Hartsell July 31, '1951 2,672,383 Hamer Mar. 16, 1954 2,672,934 Min'er Mar. 23, 1954 2,689,008 Allen et al. Sept. 14, 1954 2,693,856 Allen Nov. 9, 1954 2,708,876 Nowak May 24, 1955 2,718,264 Allen et al. Sept. 20, 1955 2,766,828 1956 Rachford Oct. 16, 

